You have:

use strict;
[download]

which enabels strictures, see perldoc strict. You need to declare variables before using them, e.g. my $input;. Copying and pasting other peoples code without understanding it is a bad idea. Consider spending some time working your way through the following links:

• perlintro
• http://learn.perl.org
• http://perldoc.perl.org
• The tutorials section of this site, Use strict warnings and diagnostics or die, Debugging and Optimization

Update: Also, don't ignore previous advice. See the responses to Re^2: How to get input text boxes populated.